Turbochargers are generally used to enhance operability of a device. For example, in the context of turbine engines, turbochargers may be used to heat a volumetric flow of engine exhaust gas to pressurize or boost an intake air stream into a combustion chamber. In this regard, exhaust gas from the engine may be routed into a turbocharger turbine housing within which a turbine is mounted. The exhaust gas flow impinges against the turbine to cause it to spin. Because the turbine is mounted on one end of a shaft that has a radial air compressor mounted on an opposite end, rotary action of the turbine also causes the air compressor to spin. The spinning action of the air compressor causes intake air to enter a compressor housing and to be pressurized or boosted before the intake air is mixed with fuel and combusted within an engine combustion chamber.
To reduce friction between and to extend the useful lives of the rotating components of the turbocharger, foil bearings may be used to support rotating components of the turbine engines, turbochargers, and the like. Generally, a foil bearing includes a journal mounted to the rotating component and a cylindrical top foil disposed around the journal. The journal and top foil are configured such that when the rotating component rotates at an optimum operational speed, the foil and the journal separate from each other to form an air gap. As the air gap between the foil and the journal grows, pressurized air is drawn in to serve as a load support and act as a lubricant to the rotating component and surrounding static components.
In the absence of the pressurized air between the journal and the top foil, the two components may come into contact with each other or with other surrounding components. Thus, to protect the components from premature wear, one or more of the components may include a coating thereon. The coating may having a formulation that includes one or more solid lubricant constituents, such as a graphite fluoride/polymer composites, molybdenum disulfide, silver, calcium fluoride, and/or ternary carbide and nitride materials. To bond the solid lubricant constituents to the substrate, one or more bonding constituents may be included in the coating formulation.
In the past, fluorides have been used as bonding constituents. However, under certain conditions, they may undesirably at least partially decompose the component to be coated during processing. Other bonding constituents, such as eutectics have been employed in other formulations. However, application of coating formulations that include the eutectics may not be used in certain coating formation processes (such as sintering processes) that are limited to low processing temperatures (e.g., about 1000° C.). Specifically, a temperature representing a softening point of the eutectic portion of the coating formulation may exceed the low processing temperature limits.
Hence, there is a need for a method for coating turbocharger components that does not affect the component to be coated and that may be used in low temperature coating processes where processing temperatures may be limited to about 1000° C. Additionally, there is a need for a coating that has improved oxidation-resistance, as compared to conventional coatings. Moreover, it is desirable for the methods of manufacturing the coating to be relatively simple and inexpensive to perform.